London, Sep 16 (IANS) An 18-year-old youth was arrested on Saturday in connection with the terror attack on a London Tube train a day earlier, that left 29 people injured and resulted in an increase in the country’s terror threat level from “severe” to “critical”.

The youth was detained in the port area of Dover by Kent Police over the Friday morning rush hour attack at the Parsons Green station in southwest London, BBC reported.

The man, whose identity and nationality have not been disclosed, was charged under section 41 of the Terrorism Act, with an act of terror, officials said.

Metropolitan Police Deputy Assistant Commissioner Neil Basu said the arrest was “significant”, but the terror threat level remains at “critical” and the investigation continues.

“This arrest will lead to more activity from our officers. For strong investigative reasons we will not give any more details on the man we arrested at this stage,” he said.

Home Secretary Amber Rudd will be chairing a meeting of the government’s Cobra emergency committee later.

The Islamic State group on its Amaq news agency claimed it was behind the explosion, which took place at 8.20 a.m. on Friday and sent a ball of fire along a carriage of the eastbound District Line train from Wimbledon at the Parsons Green station, southwest London.

The explosion occurred through a homemade explosive artefact, inside a white bucket, which failed to fully detonate. Less than 24 hours later, the suburban Tube station was back in use by travellers.

Hundreds of police officers were scouring CCTV footage, questioning dozens of witnesses and studying the remnants of the device in search of clues to the identity of those responsible.

Prime Minister Theresa May, raising the terror status to its highest level, which means another attack is considered imminent, said late on Friday that military personnel would replace armed police “on guard duties at certain protected sites which are not accessible to the public”.

Metropolitan Police’s Assistant Commissioner Mark Rowley asked the public to remain “vigilant”, but said people should “not be alarmed”. When asked about possible IS involvement, Rowley told reporters that it is “routine” for the extremist group to take responsibility for attacks in “these sorts of circumstances,” regardless of its actual involvement.

Commuters described a “fireball” sweeping through their District Line carriage, burning off some victims’ hair and leaving some with severe burns. The blast sparked a stampede of passengers attempting to flee the station, threatening to crush a pregnant woman and children caught in the panic.

British media reported that the crude device, carried in a bucket and shoved into a shopping bag, had a timer, suggesting that some degree of bomb-making knowledge was employed.

Police swiftly declared the explosion as a “terrorist” incident, but have not confirmed any details of suspects after US President Donald Trump claimed the perpetrators were “in the sights of Scotland Yard”.

The Metropolitan Police dismissed the US President’s “speculation”, while May said the intervention was “not helpful”. This is the fifth terrorist attack in Britain in less than six months.